Process of bonding nonwoven fabric with chlorinated atactic polypropylene and the bonded fabric



United States Patent 3,316,122 PROCESS OF BONDING NONWOVEN FABRIC WITHCHLORINATED ATACTIC POLYPRO- PYLENE AND THE BONDED FABRIC Walter B.Armour, Plainfield, N.J., Gerald H. Brown, Syracuse, N.Y., and Emil D.Mazzarella, Plainfield, NJ., assignors to National Starch and ChemicalCorporation, New York, N.Y., a corporation of Delaware No Drawing. FiledFeb. 20, 1964, Ser. No. 346,092 8 Claims. (Cl. 117-136) This inventionrelates to novel binding compositions for use in the preparation ofnonwoven fabrics. More particularly, it relates to the preparation ofnonwoven fabrics which are characterized by their excellent fireretardancy as well as by their unusual degree of softness and strength.

Nonwoven fabrics are fabrics which are neither woven, knitted, spun normade by conventional wool felting processes. They are, instead, built upthrough the interlocking of fibers by means of chemical bonding agentsor fusible fibers. This is accomplished by any combination of mechanicalmeans, chemical action, or heat. Nonwoven fabrics may thus be broadlydefined as a textile structure consisting of a Web or mat of fibers heldto gether with a binding material.

In preparing these nonwoven fabrics it is possible to use either naturalor synthetic fibers. Thus, among the fibers which may be used innonwoven fabrics are cotton, rayon, cellulose acetate, and triacetate,nylon, acrylic, polyester, glass, vinyl polymer and copolymer fibers, aswell as paper fibers, wood pulp fibers, and fibers derived from wastepaper. Generally, different types of fibers are blended in order toachieve the desired end product properties. After being blended, theindividual fibers are then picked or shredded so as to obtain a moreuniform distribution. These initial operations serve to prepare thefibers for the web forming process which employs various complex webforming machines. These machines produce a web or flimsy sheet of fiberswhich will not remain in one piece by itself, but has to be sup portedby conveyors.

At this point in the process, the web must be bonded and this may beaccomplished by mechanical means which entangle the fibers and thus givestrength to the web. However, binding is more usually accomplished bythe use of a chemical binding agent which may be in the form of anemulsion, a powder, a solvent, or a solution. These binding agents canbe applied to the nonwoven web by immersion, spraying, in the form of afoam, by rolls or pads, or by the sprinkling of dry thermoplasticresins. The web can be completely covered with the binding agent or thebinding agent may be applied so as to form a discontinuous pattern byprocesses similar to printing. Thermoplastic fibers may also be used toaccomplish binding by being blended into the fiber mixture or by usingthem as the sole component of the web. Application of heat causes thesefibers to become tacky and thus stick to each other and/or to othernon-thermoplastic fibers,

The formation of a nonwoven gauze difiers, in some respects, from thepreparation of a nonwoven fabric. Rather than being formed into a web,the fibers are, instead, made into yarns which are aligned parallel toeach other. These yarns, which represent the warp yarns of the gauze,are then run through a saturation bath wherein a series of steel conesmechanically meter the amount of binding agent that is applied to thewarp yarns. The wet warp yarns are thereupon adhered to a series of fillyarns which comprise parallel aligned yarns positioned perpendicularlywith respect to the wet warp yarns. The complete gauze is then dried byany suitable means such as by being passed over a drying drum or aheated calendar stack.

Various materials have been employed as binding agents for nonwovenfabric and gauze, including such binders as polyvinyl acetate,polyacrylates, polyvinyl chloride, ureaformaldehyde resins, and thelike. None of these binding agents, however, have been entirelysatisfactory, primarily because of prohibitive costs and/orunsatisfactory properties imparted to the resulting nonwoven products.

Thus, for example, it is well known that many of the binding agentsheretofore utilized have provided nonwoven fabrics with very little, ifany, resistance to fire and flame propagation and, in some cases, thesebinders have even served to increase the flammability of the fabric.Fire resistance is, of course, of great importance in nonwoven fabricswhich are to be used in either consumer or industrial applicationswherein they may tend to become accidentally ignited. Unfortunately, inat tempting to provide binders which successfully imparted fireretardancy, it was found that the binders which were desirable in thisrespect were often deficient with regard to their adhesive an-d/ orprocessing characteristics.

In addition to the above described fire retardency problem, waterresistance, tensile strength, edge tear, and elongation of nonwovenproducts have often proved deficient when binders heretofore known havebeen utilized. Moreover, since nonwoven fabrics are widely use-d inwearing apparel, upholstery, floor and wall coverings, and similarapplications, it is often desirable that such fabrics possess a degreeof softness, or, as it is commonly referred to, a good hand or feel.This latter property has often lacking in nonwoven products when thebinding agents of the prior art have been used in their manufacture.

Thus, it is an object of this invention to provide binding compositionsfor nonwoven fabrics and gauze, the use of which results in no nwovenmaterials which are characterzed by their outstading resistance to fireand flame propagation as well as by their desirable characteristics ofwear and feel. Other objects and advantages of this invention will beapparent from the discussion which follows hereinafter.

We have now discovered that the use of chlorinated atactic polypropyleneas a binder for nonwoven fabrics provides the resulting products withoutstanding fire retardancy properties. In addition, the use of thisnovel binder imparts highly desirable properties of water resistance,tensile strength, edge tear, and elongation to said fabrics and alsoprovides them with a remarkable degree of softness. Moreover, the latterchaarcteristic of softness of hand is realized without any sacrifice inthe strength of the resulting nonwoven products.

In accordance with the invention, nonwoven products are prepared bymeans of a process involving the application, to a nonwoven sheet or webof fibers, of a binder composition comprising chlorinated atacticpolypropylene which may be in the form of either a lacquer or an aqueousemulsion.

Polyproplylene is a synthetic resin which, of late, has enjoyed greatlyincreased usage in the preparation of molded articles, fibers and films.For use in the late applications it is desirable that the polypropyleneshould have a highly crystalline structure which thereby serves toincrease the strength of this versatile plastic. The inherentcrystallinity of polypropylene, is in turn, dependent upon its molecularstructure or configuration. Thus, crystalline propypropylene molculeswill exhibit a socalled isotactic structure wherein the methyl groupswill be regularly distributed on the same side of the polymer a a a;chain in a manner analogous to that shown in the folintroduced therein.The sulfuryl chloride is then slowly lowing diagram: added with thesolution being maintained at reflux for a CH2 CH CH2 On the other hand,polypropylene which is not crystalperiod which may range from about 5 tohours, thereline will exhibit a so-called atactic structure wherein theby yielding the desired chlorinated atactic polypropylene.

methyl groups are randomly distributed on either side It may be notedthat the above described chlorination of the polymer chain in a manneranalogous to that shown procedure may also be utilized with thionylchloride.

in the following diagram. However, when gaseous clflorine is used, thisprocedure CH3 CH3 CH3 I l I CH CH CH CH CH CH CH CH CH C 2 CH CH CH Inmanufacturing polypropylene, the processes curis modified somewhat inthat the reaction temperatures rently employed make use of so-calledstereospecific are maintained below reflux levels. catalysts which arechosen for their ability to provide In using chlorinated atacticpolypropylene as the bindthe resulting polypropylene with an isotacticstructure ing agent in the manufacture of nonwoven fabrics, there andthereby impart a maximum degree of crystallinity to are several possibletechniques for their application to the polymer. However, despite theuse of these catalysts, the fiber web. These include saturation bonding,wet-roll present polymerization techniques still produce a productbonding, spray bonding, and segmental bonding. Saturawith a significantproportion of atactic polypropylene. tion bonding, which is alsoreferred to as continuous, im-

The presence of this non-crystalline fraction would, of mersion,solution or impregnation bonding, is the most course, detract from thestrength of any articles manucommonly used bonding method and consistssimply of factured from such polypropylene. Therefore, it is the passingthe fragile fiber web through a liquid binder bath.

practice in the art to separate this atactic portion from The web isthen passed through squeeze rolls to remove the crystalline material andthis is readily accomplished the excess binding agent. Wet-roll bondingis similar by means of a solvent extraction technique. To date, to thesaturation process, the main difference being that very few, if any,applications have been found for this the web does not go through theliquid bath. Instead, a atactic polypropylene residue. Its inherent lackof crystalseries of mechanical rolls pick up the binder and translinityobviates its use in the preparation of films, fibers, fer it to themoving web. Spray bonding applies the and molded products; while any useof this material as liquid binding agent by spraying a fine mist ofbinder over an adhesive base is similarly precluded since the resultthesurface of the web. And, segmental bonding, which ing adhesive films areexceeding soft and display relatively is also referred to asdiscontinuous, patterned, print, enlittle strength. graved,intermittent, and spot bonding, is the process The chlorinated atacticpolypropylene which is used as wherein the binding agent is applied tothe web in a unithe binding agent in the process of our invention ispreform pattern, resulting in definite bonded and unbonded pared bydissolving the atactic polypropylene in a nonreactive organic solventsuch as carbon tetrachloride,

portions upon the web surface.

With the above described application techniques, or

methylene chloride, chlorobenzene, or chloroform. The with any otherprocedures which may be devised by the atactic polypropylene is thenchlorinated in the presence practitioner, it is desirable that thefinished nonwoven of a suitable catalyst which may be a solvent solubleorfabric or gauze contain from about 3% to 2 80% of ganic peroxide, suchas benzoyl peroxide or lauroyl perbinding agent, i.e., chlorinatedatactic polypropylene oxide, or a metal salt, such as ferric chloride oraluminum solids, as based on the weight of the dry fibers in thefinchloride. :The latter catalysts are usually present in the ishednonwoven product. Particularly effective fabrics reaction mixture in aconcentration of about 0.1 to 1.0%, were obtained wherein the finishedproduct contained by weight, of the atactic polypropylene undergoingchlorifrom about to 200% of binding agent. The desired nation.Chlorination may be accomplished by bubbling binder content can berealized by proper adjustment of chlorine gas directly onto the reactionmixture or by rethe solids content of the binding agent lacquer oremulfluxing the latter in the presence of a chlorination agent sionand/or by varying by means well known to those such, for example, assulfuryl chloride or thionyl chloskilled in the art, the initial pickupby the fiber Web or ride. warp yarns of the binding agent.

For use as a binding agent in the Process of 6p Subsequent to theapplication of our chlorinated Vention, the chlorinated atactic P yp p y0 atactic polypropylene binding agent, the sheet or web of lain fromabout 8 to about 35%, by Weight, of chlorillenonwoven fabric may bedried at room or elevated tem- A typical procedure, in this caseemploying sulfuryl peratures. The drying cycles used in this processdepend chloride, which may be utilized for the chlorination of upon thetemperature employed, the rate and amount of atactic polypropylene wouldinvolve first preparing an orair flow, and other factors inherent in thepractitioners ganic solvent solution of the atactic polypropylene withfacilities and method of operation. In any case, temthe process ofsolution being assisted by subjecting the peratures varying from roomtemperature to about 350 mixture to mechanical agitation as Well as byheating it P, may the used to remove the solvent or water that is toreflux. While the thus prepared solution is mainpresent in the wet web.

tained under reflux and agitation, the selected catalyst is 7 When thebinders of our invention are utilized in the form of laquers, it ispossible to use various solvents in their preparation. Thus, forexample, chlorinated atactic polypropylene may be dissolved in a varietyof solvents, including: aromatic hydrocarbons, such as toluene andxylene; cyclic hydrocarbons, such as decahydronaphthalene andtetrahydronaphthalene; aliphatic hydrocarbons containing from 5 to 11carbon atoms, such as pentane, hexane, and nonane; and, chlorinatedhydrocarbons, such as methylene chloride, carbon tetrachloride,tirichloroethylene, perchloroethylene, and also chlorinated aromatichydrocarbons such as chlorobenzene. It should be noted that, where sodesired by the practitioner, it is possible to prepare these lacquerswith various combina tions of any of the above listed solvents. Theresin solids content of these chlorinated atactic polypropylene lacquersshould usually range from about 1% to about 50% by weight.

When the chlorinated atactic polypropylene is employed in our inventionin the form of an aqueous emulsion, the latter may be prepared by addingan aqueous solution of an emulsifying agent, such as polyvinyl alcohol,morpholine-oleic acid mixtures, and the like, to an organic solventsolution of chlorinated atactic polypropylene; the latter solutionhaving been prepared by the use of any of the above listed solvents.Water is then added with vigorous agitation, the amount of water addeddepending upon the solids content desired in the ultimate emulsion. Inthose cases where the organic solvent has a boiling point less than thatof water, it can be removed from the emulsion by distillation or otherappropriate means. The resin solids content of these chlorinated atacticpolypropylene emulsions usually ranges from about 2 to 65%, by weight.

It should be mentioned that various additives, such as defoamers,lubricants, antioxidants, and the like, may be added to our chlorinatedatactic polypropylene binder formulations in order to enhance theproperties imparted to the nonwoven fabrics to which said binders areapplied. It may also be noted that our chlorinated atactic polypropylenebinders may be used in combination with various thermosetting andthermoplastic resin binders.

In the following examples, which further illustrate the embodiment ofour invention, all parts given are by weight unless otherwise indicated.

Example I This example illustrates the preparation of fire retardantnonwoven fabrics using lacquers and emulsions of chlorinated atacticpolypropylene as the binding agents therefor.

In this example, and in the examples that follow, the same basicprocedure was utilized in preparing the nonwoven fabric. In this basicprocedure, a web was bonded as it passed through the nip of a padder,the binding agent being applied by a stainless steel transfer roll whichdipped into a pan containing the binding agent and transferred theimpregnant to the passing web. The amount of binding agent picked up bythe web was determined by the pressure at the nip as well as by theinitial solids content of the binding agent. The wet web was then passedinto a forced draft oven and dried at 300 F. for a period of 3 minutes.This drying operation effected a complete removal of water or solventand the web was thereupon cooled to room temperature.

(a) 4 parts of oleic acid and 4 parts of morpholine were added to 100parts of a 40% hexane solution of chlorinated atactic polypropylenehaving a chlorine content of by weight. 85 parts of water were thenadded with vigorous agitation. The hexane was removed from the emulsionby distillation, and the solvent-free emulsion was diluted with water toa final concentration of 1%, by weight, of chlorinated atacticpolypropylene solids. A nonwoven sheet composed of 95/5 rayon/cellulosefibers was passed through this emulsion, squeezed between rollers, anddried at room temperature. In this case, the nip pressure was adjustedso as to yield a finished fabric containing 3%, by weight, ofchlorinated atactic polypropylene solids, as based. on the dry fiberweight.

(b) A nonwoven sheet composed of /5 rayon/cellulose fibers was passedthrough a 2%, by weight, hexane lacquer of chlorinated atacticpolypropylene having a chlorine content of 30%, by weight. The sheet wasthereafter squeezed between rollers, and dried at room temperature. Inthis case, the nip pressure was adjusted so as to yield a finishedfabric containing 3%, by weight, of chlorinated atactic polypropylenesolids, as based on the dry fiber weight.

Example II Medium for Percent resin Percent resin solids Binding Agentsolids or" medium content of resulting nonwoven fabric Aqueous emulsion1 3 Hexane lacqueL 2 8 Aqueous emulsiom 40 20 Hexane lacquer: 50 25Aqueous emulsion. 65 280 Hexane lacquer 50 280 The nonwoven fabricsproduced by using each of the formulations given above exhibitedoutstanding properties of fire retardancy and strength and wereremarkably soft to the touch.

Example III This example illustrates the vastly improved results withrespect to a number of different properties in addition to fireretardancy, obtained by using chlorinated atactic polypropylene as thebinding agent for nonwoven fabrics, as compared to the results obtainedby using a number of conventional binding agents under the sameconditions.

(a) The basic procedure of Example I was employed to prepare a number ofviscose fiber nonwoven fabrics, each of which was bound with a differentbinding agent. In each case, the binding agent solids constituted about50% by weight of the resulting fabric, as based on the weight of the dryfibers. The table appearing below sets forth the binding agents used,along with certain prop erties exhibited by the fabrics thereby bound.

In determining the edge tear and percent elongation of the fabricstested, test procedures established by the Technical Association of thePulp and Paper Industry (TAPPI) were followed. The Finch edge tear wasdetermined by means of TAPPI test T-470M-54, wherein higher readingsindicate a proportionately stronger fabric. The percent elongation wasdetermined by means of TAPPI test T457-M-46.

The test for stiffiness was carried out on an instrument called theGurley Stiffness Tester. In using this instrument, a sample of thefabric 1 inch wide and 1.5 inches long was clamped centrally on theprojected arm of the machine with the length of the sample being in avertical position. This sample extended parallel to a freely swingingpointer to which various weights were fastened. As weights were added,the arm with the clamped sample pressed against and moved the pointer,thereby giving a reading in milligrams which comprises the Gurleystiffness, wherein a higher reading indicates a. proportionatelystilr'er and less desirable fabric.

Medium for Gurley Finch Percent Binding Agent Binding Agent I'IandStifiness Edge Elontnig.) Tear gation (lb/in.)

Polyvinyl acetate Emulsion Poor I, 400 2. 3 18 Polyvinylidene chloride d824 4.3 22 :80 vinyl acetate :ethyl aerylate coploymer 444 6.8 44 75:25butadienezacrylonitrile oopolyiner 380 7. 8 55 Chlorinated atacticpolypropylene (10%, by 230 13.0 84

weight chlorine content).

From the results represented in the above table, it can be seen that theuse of chlorinated atactic polypropylene as the binding agent fornonwoven fabrics presents significant advantages over the use of any ofthe conventional binding agents listed above.

Example IV The following example illustrates the actual preparation of anumber of samples of chlorinated atactic polypropylene lacquers whereineach of the respective samples had a different chlorine content. Theselacquers were then converted to aqueous emulsions which were used forthe preparation of fire retardant nonwoven fabrics by means of the basicprocedure described in Example I. It may also be noted that the varioussamples of chlorinated atactic polypropylene whose use was described inExamples I, II and III were all prepared by means of the processdescribed below.

Using gaseous chlorine and sulfuryl chloride as chlorination agents, Weprepared several chlorinated atactic polypropylene lacquers each ofwhich had a resin solids content of by weight. In preparing theselacquers, the chlorination procedure described earlier in thespecification was utilized. The resulting lacquers were then convertedinto aqueous emulsions by adding an aqueous solutiOn of an emulsifier tothe lacquer while subjecting the latter to vigorous agitation. In eachcase, we used 6%, of emulsifier as based on the weight of chlorinatedatactic polypropylene in the respective lacquers. These emulsions, eachof which had a resin solids content of 5%, by weight, were then used asbinding agents for the preparation of nonwoven fabrics by means of thebasic procedure described in Example I.

In the following table are presented details relating to the preparationof the various chlorinated atactic polypropylene lacquers and theirsubsequent conversion to Summarizing, this invention provides thepractitioner with fire retardant nonwoven products through the use ofnovel binders comprising chlorinated atactic polypropylene. Variationsmay be made in proportions, procedures and materials without departingfrom the scope of the invention which is limited only by the followingclaims.

We claim:

1. The process of making a bonded nonwoven fabric characterized by itsresistance to fire, softness and strength, said process comprisingapplying to a web of fibers a binding agent consisting essentially ofchlorinated atactic polypropylene dispersed in a liquid medium.

2. The process of claim 1, wherein said chlorinated atacticpolypropylene has a chlorine content of from about 8 to by weight.

3. The process of claim 1, wherein said binding agent is in the form ofan organic solvent solution.

4. The process of claim 1, wherein said binding agent is in the form ofan aqueous emulsion.

5. A bonded nonwoven fabric characterized by its fire retardancy,softness and strength, said fabric comprising a web of fibers bondedsolely with a chlorinated atactic polypropylene binding agent.

6. The nonwoven fabric of claim 5, wherein said chlorinated atacticpolypropylene has a chlorine content of from about 8 to 35%, by weight.

7. A bonded nonwoven fabric characterized by its fire retardancy,softness and strength, said fabric comprising a web of fibers bondedsolely with the dried residue of an organic solvent solution ofchlorinated atactic polypropylene.

8. A bonded nonwoven fabric characterized by its fire retardancy,softness and strength, said fabric comprising a web of fibers bondedsolely with the dried residue of an aqueous emulsion of chlorinatedatactic polypropylaqueous emulsions. ene.

Parts of 4 Parts of i Chlorine in l Formulation No. Atactic CatalystUsed (Parts) Chlorination Agent Chlorinating Chlorinated EmulsifyingAgent Polypro Agent Polymer pylcne 1 -s 100 Lauroylperoxide (0.3). 2 035 Polyvinyl alcohol.

100 Ferric chloride (0.3). 94 26 Do. 100 Ferric chloride and I 18 Do.Ferric chloride (0.3). 45 11 Oleic acidmorpholine. 100 0 30 S Polyvinylalcohol.

References Cited by the Examiner UNITED STATES PATENTS 3,126,297 3/1964Diamantopoulos et al. l17-140 3,192,188 6/1965 Orthner of al 260-8823,228,791 1/1966 Armour et a1 117--138.8

WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner.

1. THE PROCESS OF MAKING A BONDED NONWOVEN FIBRIC CHARACTERIZED BY ITSRESISTANCE TO FIRE, SOFTNESS AND STRENGTH, SAID PROCSS COMPRISINGAPPLYING TO A WEB OF FIBERS A BINDING AGENT CONSISTING ESSENTIALLY OFCHLORINATED ATACTIC POLYPROPYLENE DISPERSED IN A LIQUID MEDIUM.